The purpose of this contract is to provide support for the development and evaluation of the logical models and structures required to create a Unified Medical Language System (UMLS). Central UMLS components will be: (1) a Metathesaurus which will store biomedical concepts and terms in a canonical form to which multiple existing vocabularies and classifications will be mapped and (2) an Information Sources Map or Directory which can be used to identify and locate the biomedical information source(s) appropriate to a particular user's query. Direct users or computer applications will be able to select individual UMLS features or combinations of features to interpret questions, identify appropriate information sources, translate queries into a variety of different target vocabularies, and retrieve, evaluate, and organize information relevant to a particular query. The goal is not to impose a single vocabulary on all systems and users but to make the myriad of classifications of biomedical knowledge invisible to the user while providing a single logical path to a broad range of automated biomedical information. The contractor shall provide to the National Library of Medicine (NLM) personnel qualified to perform, and facilities and materials necessary to provide technical and intellectual services on a task assignment basis in support of the UMLS program.